Project summary: This project investigates glial control of adenosine levels and its role in sleep homeostasis. Sleep homeostasis, the drive to sleep based on prior waking time, is reflected by increased slow wave activity (SWA, 0.5-4.5 Hz oscillation in electroencephalographic activity) following prolonged waking and decreased SWA following SWS. This dissipation in SWA during SWS and buildup of SWA following prolonged waking has been demonstrated in humans, rats, and mice. Further, SWA accumulation and dissipation has been modeled in wildtype and mutant rodents and it is known that SWA accumulation and dissipation is under genetic control. In the current project, the role of adenosine in SWA homeostasis is investigated, first by using a genetic knockout of adenosine A1 receptors (AdoA1R), the main adenosine receptor through which adenosine influences SWA, and secondly by using an inducible knockout of adenosine kinase (AdK), which converts adenosine to AMP and, due to equilibrative transporters, largely controls the extracellular level of adenosine. Adenosine kinase is expressed primarily in glia in adult animals and therefore, if adenosine influences SWA homeostasis, as we hypothesize it does, this would demonstrate glial control of SWA homeostasis. The project uses 3 specific aims to: 1) characterize the role of AdoA1Rs in SWA accumulation and dissipation under baseline and recovery from sleep deprivation conditions, 2) characterize the role of glial AdK in AdoA1R mediated inhibitory tone on mammalian cortical neurons, and 3) characterize the role of glial AdK in accumulation and dissipation of SWA under baseline and recovery from sleep deprivation conditions. Overall, these specific aims investigate one potential neurobiological substrate, adenosine, which may influence the SWA accumulation and dissipation that is indicative of the sleep drive. Adenosine is known to influence SWA so it is reasonable to test this compound as a neurobiological substrate that controls SWA homeostasis. Preliminary data support a role of AdoA1R in SWA homeostasis and suggest glial-mediated AdK knockout, which increases adenosine levels, also alters SWA homeostasis but in the opposite direction as AdoA1R knockout. These findings will provide a mechanism for glial control of behavioral state related SWA that is sensitive to glial metabolic state.